The invention relates to an apparatus for the production of fine mineral fibres, in particular glass fibers and diabase fibres by the nozzle blast process. Apparatus of this type comprise a melt crucible with a number of outlet openings from which primary filaments issue and are separated into fibres in a converging/diverging draw nozzle by means of a blowing medium sucked into the draw nozzle. A subsonic diffuser for reducing the flow rate is then connected to the diverging portion of the draw nozzle.
The nozzle blast process is characterised in that melt streams flow out of a crucible containing the mineral melts under the influence of gravity and are separated into fibres in a draw nozzle under the influence of gas flowing at a high flow rate substantially parallel to the melt streams, are extracted and cooled below the softening temperature. This is in principle a very old process which has already been described in German Pat. Nos. 694 182 and 803 925. More recently, the nozzle blast process has been further developed and refined (see EP No. 66 506 and EP No. 38 989).
The diameter of the fibres produced by the nozzle blast process are generally of the order of a few .mu.m. Problems arise if fibers having a diameter smaller than 1 .mu.m are to be produced. Tests on conventional apparatuses to obtain finer and finer fibres by adjusting the operating parameters have not yet led to the desired result. Instability (frequent tearing of fibres and occurrence of beads of melt) is observed and this leads to an irregular product which cannot be tolerated. The invention starts from here.